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Are quantum no-go theorems overrated/potentially counterproductive?

  1. Oct 27, 2013 #1
    Based on my own frustration with trying to reconcile the validity of some of the assumptions of the Von Newman, Bell's, Kochen-Specker, PBR theorem, etc., and other quantum no-go theorems, I thought these were some interesting papers critically discussing this topic:
    Against the ‘No-Go’ Philosophy of Quantum Mechanics
    http://philsci-archive.pitt.edu/100...antum_mechanics,_Revised_authored_version.pdf

    Khrennikov arguing from a somewhat different perspective reaches a somewhat similar conclusion:
    Bell argument: Locality or Realism? Time to make the choice.
    http://arxiv.org/pdf/1108.0001.pdf
    Vaxjo Interpretation of Wave Function: 2012
    http://arxiv.org/pdf/1210.2390.pdf
     
  2. jcsd
  3. Oct 28, 2013 #2

    Demystifier

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    I also think that it is more useful to construct models which DO reproduce predictions of quantum mechanics, then to prove general theorems telling what kind of theories can NOT do that.

    For example, in Appendix A.1 of my recent paper
    http://arxiv.org/abs/1309.0400
    I explain how several no-go theorems/arguments against existence of relativistic-covariant version of Bohmian mechanics are circumvented by my own relativistic-covariant version of Bohmian mechanics.
     
  4. Oct 28, 2013 #3
    I too found no-go theorems to be very counter productive. I'm having a very hard time getting people to even look at my research results, because they "obviously violate some no-go theorems". They don't, because no-go theorems are always very limited to what exactly the author considered to be generally true. I tried to publish a paper showing a positive result, and it was rejected (without having been read) because they had published a no-go result just before. For me, no-go theorems and dogmatic prejudice go hand in hand.

    Sorry for the little rant,

    Jazz
     
  5. Oct 28, 2013 #4

    morrobay

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    If a no go theorem is based on un realistic assumptions then it is counterproductive.
    From the second paper referenced, Locality or Realism :
    A realism assumption of pre existing measurement properties is incompatible with quantum
    theory, independent from any derivation of an inequality.
     
  6. Oct 28, 2013 #5

    cgk

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    I am not sure how useful this comment is, but if any of you would manage to create a theory reproducing quantum mechanical averages for n-particle systems[1], which is in some sense *computationally* favorable to wave function QM, you might find it easier to establish the theory indirectly via supporters in electronic structure theory, chemical dynamics, or similar fields. In such "applied quantum mechanics" fields, the main objective is generally obtaining predictions for concrete, realistic systems via approximations, and not the interpretation of fundamental QM. Since in any case many approximations are involved, people would be much more willing to adapt to new ways of doing things, if this allows for computing systems which are currently inaccessible.

    [1] It is not even requires that correspondence is exact: It just needs to provide verifiably accurate approximations for a restricted, but known, class of problems.
     
  7. Oct 28, 2013 #6

    stevendaryl

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    What has always struck me about Bell's theorem and various other no-go theorems is that they prove the impossibility of something that no mainstream physicists are trying to accomplish, anyway. The sort of hidden-variables theory that Bell proved was impossible is not a theory that anyone had seriously tried to develop, anyway.
     
  8. Oct 28, 2013 #7

    DrChinese

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    Of course No-go theorems are powerful and useful. And of course they are constraining, to the frustration of many. That they are so often applied is a testament to their utility, and not dogmatism of the part of publications.

    A good counter-example will blow away dogmatism, but please note the use of the adjective "good". So far, I have yet to see a good counter-example in any of the dozens of papers purporting same. And no, I don't read every one to "find" its flaw.
     
  9. Oct 28, 2013 #8
    In an ideal world I would agree. I would've even agreed 5 years ago. What really happens is that people don't even bother to look at your arguments, so you don't even get to the point where they're evaluated. If you make bold enough claims and your paper is not just 2 pages, you can be pretty sure that nobody is going to read it until somebody else they trust read it and promoted it.

    Physics is full of "practical" dogmatism these days. What is unlikely is not even considered, because it costs time. And this kind of subtle hostility towards new ideas is strongly supported by misunderstood or too broadly interpreted no-go theorems. And your formulation of "finding the flaw" fits this scheme perfectly. Instead of looking for flaws we should be looking for ideas.

    Cheers,

    Jazz
     
  10. Oct 28, 2013 #9

    Nugatory

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    EPR weren't actively developing such a theory, but surely at the time that they published, pre-Bell, they believed that doing so would be a useful and important effort. Although we'll never know for sure, it's plausible that Einstein would have dropped this position if he had lived to see Bell's theorem.

    Nonetheless, it would be an error to generalize from "Bell's no-go theorem is useful in guiding us away from unproductive investigations and for identifying the key experimental results that a candidate theory must predict" to "All no-go theorems are ...."
     
  11. Oct 28, 2013 #10

    Demystifier

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    Unfortunately, you are right. (Except that I don't think that 5 years ago the situation has been much different. Perhaps it was more like 50 years ago.)
     
  12. Oct 28, 2013 #11
    Yes, with the five years I was really referring to the moment when I realized it, not when it changed. I don't know if it was ever really different. There's a long history of brilliant new ideas being rejected and ridiculed at first, and often for a long time.

    Cheers,

    Jazz
     
  13. Oct 28, 2013 #12

    DrChinese

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    Well, this is a statement much like "I want to end childhood hunger". Sounds great. We all wish our original ideas would be immediately recognized and accepted.

    If only folks had looked at my last paper with a more open eye! :smile: It is ground-breaking...
     
  14. Oct 29, 2013 #13

    bhobba

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    Yes that's true. The trouble is - what to do about it? All you can really do is try and be open minded - but aside from that it just seems to be one of those things associated with being human.

    As far as the original question goes I believe no go theorems are very useful - not because what they imply is necessarily true - but disentangleing exactly what its saying can be very illuminating - eg Gleason's Theorem on the surface seems to rule out HV's - but understanding its assumption of non-contextuality is a valuable QM insight.

    Thanks
    Bill
     
  15. Oct 30, 2013 #14

    zonde

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    It does not take many pages to say that you do not make assumptions used by no-go theorem. If you can't say in a couple of sentences why no-go theorem does not apply in your situation it would be quite sound reason to stop reading further.

    I personally favour looking for flaws. However not the ones DrChinese is talking about.


    Speaking about utility of no-go theorems - their utility is not in increasing our knowledge about physical reality. They rather help to increase consistency of our ideas.
     
  16. Oct 30, 2013 #15
    It's not quite that simple. You can easily state that the usual no-go theorems do not apply. But usually the exact reason how that works is quite complicated, because otherwise it would be rather obvious and you wouldn't have to write a paper about it. In the end it's not unlikely that the entire point of the paper is to explain why the no-go theorem does not apply, so you're back where you started: To get people to actually read the paper.

    Sometimes looking for flaws is helpful, in order to gain understanding. But if someone comes up with a new idea, looking for flaws is counter productive, because usually what you think is a flaw and an actual misunderstanding of what is being argued are indistinguishable. So the first objective should be to really try to understand the idea as presented by the author, before looking for errors. In my experience the "obvious error" often is on the side of the reader.

    Yes, no-go theorems are useful. But like I said earlier they can support dogmatism. Especially if they're used as short cuts for actual thinking. I've seen no-go theorem being misapplied in discussions very often, and it took a lot of effort to set this straight, turning the whole discussion into a one about the understanding of those theorems instead of being constructive.

    Cheers,

    Jazz
     
  17. Oct 30, 2013 #16

    Demystifier

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    I agree. One of the reasons is the following. No-go theorems usually have the form:
    If conditions C1, C2, ..., Cn are fulfilled, then A is not possible.
    The problem is that people tend to forget the conditions, and remember only that A is not possible.
     
  18. Oct 30, 2013 #17

    bhobba

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    Yes - but we have the cautionary tale of Von Neumann's proof.

    He didn't explicitly state the assumption he made about the linearity of expectation values and considering his reputation people simply accepted it. A few people pointed it out but were generally ignored.

    It wasn't until Bell took up the baton it really became well known.

    My view is it behooves all of us to be careful - but as sure as death and taxes we will fail - but must try.

    Thanks
    Bill
     
  19. Oct 30, 2013 #18

    stevendaryl

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    Almost nothing in physics is conclusively proved impossible. But at some point, a consensus develops that certain ideas are not worth pursuing further. Whether that's good or bad is an open question. There are always more possible lines of inquiry than there are researchers to pursue them.
     
  20. Oct 31, 2013 #19

    zonde

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    Hmm, are you sure it's related to no-go theorems? Have you other experience with another paper that does not involved no-go theorems and when it was easy to get people to read the paper? Maybe it's rather your argumentation skills. Look what you wrote:
    A lot of hand waving without any solid argument. But if I try to understand your idea without paying attention to poor arguments (I should judge new ideas by how they improve my understanding) it turns out that your idea is still no better - a lot of effort but result is still the same.

    Yes you said that no-go theorems can support dogmatism. But you are not telling why. You can misapply ordinary theorems too - this is not an argument.
     
  21. Oct 31, 2013 #20

    strangerep

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    I must agree with that. A wise man told me some time ago that if an author cannot express themselves clearly and concisely, they probably have nothing valuable to say anyway, and the effort of trying to follow their paper is likely a waste.

    You could call that wisdom a "no-go" theorem, for which I have yet to find a counter example. :wink:
     
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